1. Field of the Invention:
The present invention relates to a method of performing three-dimensional exposure and an apparatus for performing three-dimensional exposure, for instance, to a method and an apparatus by use of three-dimensional photolithography employed for transferring an image to a recording medium among a series of processing works of practicing groove-processing, etc., corresponding to the image by utilization of photo-etching technology or the like.
2. Description of the Prior Art:
Generally, in the groove processing technology of a non-contact axis employed for making hydrodynamic gas bearing, or in the etching technology of processing a cap of fountain pen, a photo-sensitive coating film, that is, a photo-resist coating film is formed on a surface to be three-dimensionally-processed, and thereafter the photo-sensitive coating film is exposed to the ultraviolet rays through an image carrying film or a mask. Conventionally, various sorts of three-dimensional exposing method have been adopted for transferring an image of predetermined shape onto a surface to be processed, and various sorts of three-dimensional exposing device have been employed corresponding thereto.
As to such conventional sorts of three-dimensional exposing method and apparatus, there are several prior art documents. For instance, the conventional sorts of three-dimensional exposing method and apparatus are described in "A Three-dimensional Optical Device" by D. M. Allen, et al. (Annals of the CIRP Vol. 36/1/1987); a published specification of Japanese laid-open patent application, Tokkaisho 52-11143/1977(SHOWA); and "A Gas Bearing--from designing to manufacturing" by Shinichi Tohgoh, published on Dec. 25, 1984.
A cylindrical work constructs an axis portion of the afore-mentioned hydrodynamic gas bearing, and a photo-sensitive coating film is formed on the outer circumference of the cylindrical work. A mask closely surrounds the outer circumference of the work holding the photo-sensitive coating film therebetween. An image to be transferred to the photo-sensitive coating film is formed on the photo-mask. A mercury-vapor lamp is employed as an exposure light source. Ultraviolet rays emitted from the mercury-vapor lamp pass through a convex lens and are converted to parallel light rays, and a part of the parallel light rays is projected onto the photo-mask through a slit of a light intercepting plate disposed between the convex lens and the work. On the other hand, the work rotates around the axis of the work together with the photo-mask. The photo-sensitive coating film of the work is exposed in order to the photo-sensitive coating film through the image of the photo-mask. In such a way, the image on the photo-mask is transferred onto the photo-sensitive coating film 2.
Hereupon, such exposing method is called "a slit exposing method", and the necessary exposing time Tcyl of the cylindrical body can be expressed by the following equation: ##EQU1## Here, Tp, D and W respectively signify as follows: Tp; Adequate Exposure Time of Photo-Resist formed on the Surface of the Photo-Sensitive Coating Film 2
D; Outer Diameter of a Cylindrical Body formed by the Photo-Sensitive Coating Film 2 PA1 W; Width of the slit 7
Next, the afore-mentioned second embodiment of the prior art is a modification of the slit-exposure method shown in the first embodiment of the prior art. In the second embodiment, such apparatus performing slit-exposure is constructed such that an image-carrying film is transported sideways along the light intercepting plate through the gap between the light intercepting plate and the work, and the work is synchronously rotated so as to allow the circumferential speed of the work to coincide with the transporting speed for the image film. And further, a cylindrical cover is tightly attached to the outer circumference of the work so as to come into close contact therewith and fixed on the outer circumference thereof, and the slit of the light intercepting plate and the slit of the cover are made to coincide with each other on the optical axis of the parallel light rays in order to prevent the light rays from scattering at the time of exposure. And further, in the third embodiment of the prior art, a comparatively simple exposure method is practiced, e.g., a photo-sensitive coating film is formed on the surface of a platestate work, and a photo-mask having a predetermined image developed thereon is brought into close contact with the surface of the work, and further exposure is done by directly radiating the ultraviolet rays from the light source.
However, in such conventional three-dimensional methods and apparatuses, since the time of exposure is long in all cases and further the preparatory works performed before exposure mainly consist of manual operation, improvement of processing accuracy for manufacturing the products needs a high degree of skill and preparatory works expend a long time. For this reason, the efficiency of such works is lowered and it results in cost-up of the products in its turn. Those matters are thought to be defects of the conventional technology.
Namely, in the first embodiment of prior art, the afore-mentioned equation (1) shows that, in the case of employing same photo-resist(s) and presuming the outer diameter D of the photo-sensitive coating cylindrical body to be constant, the time period of exposure Tcyl is determined in the first meaning in accordance with the width of the slit formed in the light intercepting plate, and when the width of the slit is made narrower for the purpose of improving the quality of products with a high exposure accuracy, the time period of exposure is made extraordinarily long, for instance, it needs to take about thirty minutes for exposing one work. Furthermore, when the photo-mask is attached to the work, image of the photo-mask is positioned in relation to the work and the photo-mask is wound therearound. After finishing to attach the photo-mask to the work, the former has to be brought into close contact with the latter. Therefore, the preparatory works needed a high degree of skill and long time period. And further, even in the second and third embodiments of prior art, the exposure time is long on both occasions. Especially, in the third embodiment, the exposure per one work needs a considerably long time, for instance, twenty minutes. Furthermore, although an exposure method employing a laser beam has been already proposed for shortening the exposure time while keeping the exposure accuracy high, the control method is complicated and the cost of the device is high. Those matters are defects of the prior art not yet solved completely.